Although many microorganisms have been put to uses that are quite helpful to man, man has long tried to destroy other microorganisms or microorganisms in environments where their presence is considered undesirable or harmful.
In response to the need to preserve food, man has devised a variety of processes which either kill microorganisms or deny microorganisms a suitable environment for continued growth in the food and/or in containers for preserving food products. Food preservation processes used since prehistoric times include heating (cooking), smoking, salting and drying. In modern times a number of new technologies have been used in attempts to find better ways to preserve food. Some modern methods, such as microwave cooking, are merely new ways to effect an old process, i.e., heating. Other recently developed sterilization methods destroy microorganisms in a novel manner. U.S. Pat. No. 3,876,373 describes sterilizing matter by exposing the material to a plasma. U.S. Pat. No. 1,863,222 describes sterilizing food or other products by placing the material in the conductive pathway of a high frequency electrical circuit. Other methods of preserving food or the like include subjecting them to various types of radiation, such as ultraviolet light.
Most methods of processing food to inactivate microorganisms substantially alter the nature of the food. In many cases, the effect of the process on the food may prove to be quite desirable. In other cases, particularly with some of the newer technologies, the processes impart characteristics to the foods that are considered by many to be undesirable.
There are many applications where it would be desirable to preserve food without effecting any change in the food except destruction of the microorganisms which cause its eventual spoilage. For example, it would be desirable to pasteurize milk without the flavor changes attendant ordinary thermal pasteurization or the even less desirable flavor changes attendant the recently introduced process known as "ultrapasteurization". Likewise it would be desirable to prevent spoilage in meat prior to cooking for longer periods of time without freezing. In other food products, such as cheese or beer, microorganisms play an inherent role in their production; however, after a certain stage, continued growth of microorganisms is detrimental to the product. Thus, a cheese should be eaten at a certain ripeness, whereas beer is frequently pasteurized for long term bottling. The shelf life and/or palatability of such food products should be improved if the microorganism used to produce these products could be inactivated without otherwise altering the product.
Magnetic fields have been used previously in conjunction with certain food processing steps. For example, in U.S. Pat. No. 4,042,325, a magnetic field is used to maintain a laser-generated plasma. Of course, microwave cooking subjects food to a magnetic field; however, as mentioned above, the induced thermal effect kills microorganisms while substantially altering the character of the food.